Reference signal for a control channel in wireless communication network

ABSTRACT

A wireless communication terminal receives a first set of pilot signal resource elements and control information in one or more spatial layers in a first resource block in a subframe and a second set of pilot signal resource elements and data in one or more spatial layers in a second resource block in the subframe, wherein the first and second resource blocks span a set of time symbols in a sub-frame, the first resource blocks span a first set of frequency carriers in the sub-frame, and the second resource blocks span a second set of frequency carriers in the sub-frame. The terminal decodes the one or more spatial layers in which the control information is received using the first set of pilot signal resource elements, wherein the first set of pilot signal resource elements comprises a first number of pilot signal resource elements per layer. The terminal also decodes the one or more spatial layers in which the data is received in the second resource block using the second set of pilot signal resource elements, wherein the second set of pilot signal resource elements comprises a second number of pilot signal resource elements, per layer, present in the second resource block, wherein the first number is greater than the second number.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications, andmore particularly to a reference signal structure for receiving acontrol channel in a wireless communication system.

BACKGROUND

In current 3^(rd) Generation Partnership Project (3GPP) Long TermEvolution (LTE) systems, Releases 8, 9 and 10, downlink (DL) controlsignaling from a base station (or eNB) is received by a User Equipment(UE) in the first 1/2/3/4 symbols of a sub-frame. The remaining symbolsare used for receiving data. Control signaling is spread across theentire carrier bandwidth (BW) of the sub-frame and the control signalingis received by the UE on a Physical Downlink Control Channel (PDCCH).Data is received by the UE in select Resource Blocks (RBs) occupyingeither the entire carrier BW or a portion of the BW. Data is received onPhysical Downlink Shared Channel (PDSCH). The frame structure receivedat the UE is illustrated in FIG. 1.

The UE needs to perform channel estimation after receiving the PDCCH todecode the information sent on PDCCH. To perform channel estimation, UEreceives Reference Signals (RSs) or pilot symbols in the sub-frame. Thereference symbols are associated with one or more antenna ports. For LTEReleases 8, 9 and 10, the UE uses the reference signals associated withone or more of antenna ports 0, 1, 2, 3 for receiving the PDCCH. The RSstructure for antenna ports 0, 1, 2, 3 is shown in FIG. 1 whereinresource elements R0, R1, R2, R3 carry reference signals associated withantenna ports 0, 1, 2, 3, respectively. An antenna port is defined suchthat a channel over which a symbol on the antenna port is conveyed canbe inferred from the channel over which another symbol on the sameantenna port is conveyed.

For LTE Release 10 (Rel-10), for demodulating data (sent on PDSCH) theUE can either use reference signals associated with antenna ports 0, 1,2, 3 or use reference signals associated with all or a subset of otherantenna ports 7, 8, 9, 10, 11, 12, 13, 14 based on the transmissionscheme used for PDSCH reception. In 3GPP LTE, the transmission schemedepends on configuration signaling from eNB. The reference signalsassociated with these other antenna ports are typically referred to as“UE specific reference signals (UERS)” or “Demodulation referencesignals (DMRS)” or “Dedicated reference signals (DRS)”. The referencesignals associated with antenna ports 0, 1, 2, 3 are typically referredto as “Common Reference Signals (CRS)”. While the CRS are sent acrossthe entire carrier bandwidth by the eNB, DMRS can only be present inthose RBs for which the UE has a PDSCH assignment. So, for receivingPDSCH using DMRS, the UE can only use the DMRS present on those RBs forwhich it has a PDSCH assignment.

For LTE Rel-11, it is envisioned that new DL control signaling will besent by the base station to the UE in symbols that span a first slot ofthe sub-frame or in symbols that span both the first and second slots ofthe sub-frame. The new DL control signaling is generally referred to asthe Enhanced—PDCCH (E-PDCCH). Unlike the PDCCH, which is transmittedacross the entire channel bandwidth, the UE is expected to receive theE-PDCCH in a set of RBs that may span only a portion of the carrierbandwidth in the frequency domain. Also, unlike the PDCCH which isreceived by the UE using CRS, it is envisioned that the E-PDCCH can bereceived by the UE using DMRS.

The various aspects, features and advantages of the invention willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art frame structure received at a UE.

FIG. 2 is a possible LTE Rel-11 frame structure received at a UE.

FIG. 3 illustrates a wireless communication system.

FIG. 4 illustrates a schematic block diagram of a wireless communicationdevice and a companion accessory.

FIG. 5 is transmission structure for DMRS antenna ports 7, 8, 9 and 10in a resource block pair. Other DMRS antenna ports i.e., ports11,12,13,14 can be multiplexed on the same resource elements occupied byports 7, 8, 9 and 10 by using a length 4 Walsh code.

FIG. 6 illustrates HARQ-ACK turnaround time.

FIG. 7 is a first modified DMRS Structure for EPDCCH RBs.

FIG. 8 is a second modified DMRS Structure for EPDCCH RBs.

DETAILED DESCRIPTION

For LTE Rel-11, it is envisioned that new DL control signaling will besent by the base station to the UE in symbols that span a first slot ofthe sub-frame or in symbols that span both the first and second slots ofthe sub-frame. The new DL control signaling is generally referred to asthe Enhanced—PDCCH (E-PDCCH). Unlike the PDCCH, which is transmittedacross the entire channel bandwidth, the UE is expected to receive theE-PDCCH in a set of RBs that may span only a portion of the carrierbandwidth in the frequency domain. Also, unlike the PDCCH which isreceived by the UE using CRS, it is envisioned that the E-PDCCH can bereceived by the UE using DMRS.

FIG. 2 shows a sub-frame in which the UE is expected to receive E-PDCCHand PDSCH. In FIG. 2, in the vertical scale, multiple blocks offrequency also referred to as frequency carriers or frequencysubcarriers or frequency bins are shown. In the horizontal scale,multiple blocks of time (in units of OFDM symbols) are shown. Thesubframe comprises multiple resource blocks (RBs) such as Resource Block0 (RB0), Resource Block 1 (RB1), Resource Block 2 (RB2), and ResourceBlock 3 (RB3), wherein each RB comprises a plurality of subcarriers suchas 12 OFDM subcarriers over a time slot comprising a plurality of OFDMsymbols such as seven (7) OFDM symbols in 3GPP LTE for normal cyclicprefix. Typically, the subframe duration is 1 ms (14 symbols for normalcyclic prefix.) and it consists of two time slots of 0.5 ms (7 symbolsfor normal cyclic prefix.) duration each. Each RB can be further dividedinto multiple resource elements (REs), wherein each RE can be a singleOFDM subcarrier on a single OFDM symbol. In the example subframe shownin FIG. 2, E-PDCCH is sent to the UE in RB0 and PDSCH is sent to the UEin RB1 & RB3. RB2 is shown as empty in this example but RB2 can also beused to send PDSCH or E-PDCCH to the UE. Resource Blocks can be PhysicalResource Blocks (PRB) or Virtual Resource Blocks (VRB). While thedescription uses PRB to describe the control channel operation, eachphysical resource block is associated with a virtual resource block (orVRB) and the association is given by a VRB to a PRB mapping e.g. via amapping rule. The VRB index may be considered as a resource blockindexing in a logical domain. Virtual resource blocks of localized typeare mapped directly to physical resource blocks whereas Virtual resourceblocks of distributed type are mapped to physical resource blocks usingan interleaving rule. The resource allocations can be localized ordistributed, where the former may be used typically forfrequency-selective scheduling, while the latter may be targeted towardsenabling frequency-diverse scheduling.

The UE with multiple receive antennas communicating with a base unitwith multiple transmit antennas can support Multiple-InputMultiple-Output (MIMO) communication and can receive data in one or morespatial layers in one or more resource blocks (RB). The base unitprecodes the data to be communicated on a spatial layer and maps andtransmit the resulting precoded data on one or more antenna port. Theeffective channel corresponding to a layer may in general be estimatedbased on reference signals mapped to one or more antenna ports. Inparticular, in the current specification of LTE, demodulation based onDMRS (demodulation RS or UE-specific RS) is supported based on antennaports numbered as 7-14. And effective channels corresponding to each ofthe spatial layers 1-8 are mapped to each one of these antenna ports.This means that channel corresponding to a spatial layer can beestimated based on the reference signals corresponding to the antennaport associated with the layer. An antenna port is defined such that achannel over which a symbol on the antenna port is conveyed can beinferred from the channel over which another symbol on the same antennaport is conveyed.

More generally, an antenna port can correspond to any well-defineddescription of a transmission from one or more of antennas. As anexample, it could include a beamformed transmission from a set ofantennas with antenna weights being applied, where the set of antennasitself could be unknown to the UE. In this case, the effective channelcan be learned from the dedicated reference signal (or the pilot signal)associated with the antenna port. The dedicated reference signal may bebeamformed similar to the beamformed data transmission with the sameantenna weights being applied to the set of antennas. Typically, thereference signal associated with an antenna port is at least used forchannel estimation at the UE. In some particular implementations antennaport can also refer to a physical antenna port at the base unit. Areference signal associated with such an antenna port allows the UE toestimate a channel from the corresponding antenna port to the UE'sreceivers. Regardless of the actual configuration and weighting of theantennas, for purpose of UE demodulation, the channel estimated based onan antenna port(s) is the channel corresponding to the associatedspatial layer. In certain cases, the beamforming or precoding applied atthe base unit may be transparent to the UE i.e. the UE need not knowwhat precoding weights are used by the base unit for a particulartransmission on the downlink.

If a particular set of pilot signal resource elements are associatedwith an antenna port and, a spatial layer is mapped to that antennaport, then it can said that the UE receives the particular set of pilotsignal resource elements in that spatial layer.

For cases where one spatial layer in an RB is mapped to one antennaport, the number pilot signal resource elements in the RB that the UEcan use, to decode data sent in the spatial layer, is equal to thenumber of pilot signal resource elements in the RB associated with theone antenna port. This is the current operation in LTE Release-10specification and previous releases.

In a future specification, a spatial layer may be mapped to multipleantenna ports. For cases where one spatial layer in an RB is mapped tomultiple antenna ports, the number pilot signal resource elements in theRB that the UE can use, to decode data sent in the spatial layer, isequal to the sum of number of pilot signal resource elements in the RBassociated with the multiple antenna ports.

In FIG. 3, a wireless communication system 300 comprises multiple cellserving base units forming a communications network distributed over ageographical region. A base unit may also be referred to as a basestation, an access point (AP), access terminal (AT), Node-B (NB),enhanced Node-B (eNB), relay node, or by other once, present or futureterminology used in the art. The one or more base units 301 and 302serve a number of remote units 303 and 310 within a serving area or cellor within a sector thereof. The remote units may be fixed units ormobile terminals. The remote units may also be referred to as subscriberunits, mobile units, users, terminals, subscriber stations, userequipment (UE), user terminals, wireless communication terminal,wireless communication device or by other terminology used in the art.The network base units communicate with remote units to performfunctions such as scheduling the transmission and receipt of informationusing radio resources. The wireless communication network may alsocomprise management functionality including information routing,admission control, billing, authentication etc., which may be controlledby other network entities. These and other aspects of wireless networksare known generally by those having ordinary skill in the art.

In FIG. 3, base units 301 and 302 transmit downlink communicationsignals to remote units 303 and 310 on radio resources, which may be inthe time, and/or frequency and/or spatial domain. The remote unitscommunicate with the one or more base units via uplink communicationsignals. The one or more base units may comprise one or moretransmitters and one or more receivers that serve the remote units. Thenumber of transmitters at the base unit may be related, for example, tothe number of transmit antennas at the base unit. When multiple antennasare used to serve each sector to provide various advanced communicationmodes, for example, adaptive beam-forming, transmit diversity, transmitSDMA, and multiple stream transmission, etc., multiple base units can bedeployed. These base units within a sector may be highly integrated andmay share various hardware and software components. For example, a baseunit may also comprise multiple co-located base units that serve a cell.The remote units may also comprise one or more transmitters and one ormore receivers. The number of transmitters may be related, for example,to the number of transmit antennas 315 at the remote unit.

In one implementation, the wireless communication system is compliantwith the 3GPP Universal Mobile Telecommunications System (UMTS) LongTerm Evolution (LTE) protocol, also referred to as EUTRA, wherein thebase unit transmits using an orthogonal frequency division multiplexing(OFDM) modulation scheme on the downlink and the user terminals transmiton the uplink using a single carrier frequency division multiple access(SC-FDMA) or a Discrete Fourier Transform spread OFDM (DFT-SOFDM)scheme. In yet another implementation, the wireless communication systemis compliant with the 3GPP Universal Mobile Telecommunications System(UMTS) LTE-Advanced protocol, also referred to as LTE-A or some latergeneration or release of LTE wherein the base unit transmits using anorthogonal frequency division multiplexing (OFDM) modulation scheme on asingle or a plurality of downlink component carriers and the userterminals can transmit on the uplink using a single or plurality ofuplink component carriers. More generally the wireless communicationsystem may implement some other open or proprietary communicationprotocol, for example, WiMAX, among other existing and future protocols.The architecture may also include the use of spreading techniques suchas multi-carrier CDMA (MC-CDMA), multi-carrier direct sequence CDMA(MC-DS-CDMA), Orthogonal Frequency and Code Division Multiplexing(OFCDM) with one or two dimensional spreading. The architecture in whichthe features of the instant disclosure are implemented may also be basedon simpler time and/or frequency division and/or spatial divisionmultiplexing/multiple access techniques, or a combination of thesevarious techniques. In alternative embodiments, the wirelesscommunication system may utilize other communication system protocolsincluding, but not limited to, TDMA or direct sequence CDMA. Thecommunication system may be a TDD (Time Division Duplex) or FDD(Frequency Division Duplex) system. The disclosure is not intended to beimplemented in any particular wireless communication system architectureor protocol.

FIG. 4 illustrates a schematic block diagram of a wireless communicationdevice 400 comprising generally a wireless transceiver 410 configured tocommunicate pursuant to a wireless communication protocol examples ofwhich are discussed. The wireless transceiver 410 is representative of afirst transceiver that communicates pursuant to a first wirelesscommunication protocol and possibly a second transceiver thatcommunicates pursuant to a second wireless communication protocol likethe WiFi or Bluetooth protocols. In one embodiment, the first protocolis a cellular communication protocol like 3GPP LTE or some other knownor future wireless protocols examples of which were described above.

In FIG. 4, the transceiver 410 is communicably coupled to a processor420, and includes functionality 422 that controls the transmission andreception of information by the one or more transceivers. Thetransceiver also includes functionality 424 that decodes informationreceived by the one or more transceivers. These and other aspects of thedisclosure are described further below. The functionality of thecontroller is readily implemented as a digital processor that executesinstructions stored in memory 430, which may be embodied as firmware orsoftware stored in a memory device. When implemented as a user terminalor User Equipment (UE), the device 400 also includes a user interface440 that typically includes tactile, visual and audio interface elementsas is known generally by those having ordinary skill in the art. Otheraspects of the terminal 400 that pertain to the instant disclosure aredescribed further below.

FIG. 5 illustrates a transmission structure for DMRS antenna ports 7, 8,9, 10 in an RB pair. It should be understood that RSs corresponding to agroup of antenna ports may be mapped into the set of available REs usingany multiplexing method known in the art or a combination thereof, forexample, either code division multiplexing (CDM) or frequency/timedivision multiplexing where each individual antenna reference signaloccupies a different RE. For example, RSs corresponding to antenna ports7 and 8 are multiplexed using CDM and are mapped to the same REs in timeand frequency domain. Other DMRS antenna ports i.e., ports 11, 13, canbe multiplexed on the same resource elements occupied by ports 7, 8, byusing a length 4 Walsh code in time-domain. Similarly, DMRS for antennaports 12, 14 can be multiplexed on the same resource elements occupiedby ports 9 and 10 by using a length 4 Walsh code in time-domain. For LTERel-8/9/10, PDSCH resources are typically allocated to UEs in terms ofRB pairs. Given this, the UE can use pilots in both slot 0 and slot 1for PDSCH demodulation. For example, if the UE is assigned to receivePDSCH resources using antenna port 7, it can use the pilot signals senton 12 REs in the RB pair for channel estimation. E-PDCCH can be sent tothe UE only in RBs in slot 0 or in RB pairs spanning both slot 0 andslot 1. It is desirable for the UE to decode DL control information senton E-PDCCH as early as possible in each subframe to allow more PDSCHprocessing time as makes it easier for UE implementations to meetHARQ-ACK turnaround timing requirements. So, it is desirable for E-PDCCHto be sent to the UE in RBs only in slot 0.

FIG. 6 illustrates an example. Assume subframe duration is Ts ms. For aPDSCH received in subframe k UE has to send HARQ-ACK corresponding tothat PDSCH in subframe k+4. Since the PDSCH is scheduled in RB pairs, UEcannot start decoding PDSCH till the end of subframe k. Also, In orderto transmit HARQ-ACK in subframe k+4, UE has to complete PDSCH decodingand HARQ-ACK preparation before the beginning of subframe k+4. So, theUE has a maximum of 3 Ts ms for PDSCH decoding and HARQ-ACK preparation.Before the UE can start PDSCH decoding, it has to decode E-PDCCH.Decoding E-PDDCH involves searching various E-PDCCH candidates for thecandidate that contains downlink control information (DCI) specificallyaddressed to the UE. This process is also referred to as E-PDCCH blinddecoding. Although the E-PDCCH payload is typically small (<100 bits),due to blind decoding, the processing time required is non-trivial.Assume E-PDCCH decoding time is Tep ms. If the UE has to wait till theend of subframe k to decode E-PDCCH then, the UE has T1=3 Ts−Tep ms tocomplete PDSCH decoding and prepare HARQ-ACK (HARQ-ACK preparationtime). On the other hand if the UE can start decoding E-PDCCH insubframe k itself, i.e., at the end of the first slot itself (E-PDCCHearly decoding) then the UE has T1=min (3 Ts, 3.5 Ts−Tep) ms forHARQ-ACK preparation. For example, if Ts=1 ms and Tep=0.4 Ts=0.4 ms,then, without early decoding, the UE has 3−0.4=2.6 ms HARQ-ACKpreparation time. With early decoding the UE has min (3, 3.5−0.4)=min(3, 3.1)=3 ms HARQ-ACK preparation time. In this example, early decodingincreases HARQ-ACK preparation time available to the UE by 15%.

If the UE has to decode E-PDCCH only using REs in slot 0 (earlydecoding), it can only use the DMRS transmitted in the slot 0 (1^(st)slot). With the current DMRS structure, if early decoding for E-PDDCHhas to be supported, UE can only use the 6 DMRS available in the 1^(st)slot for E-PDCCH reception. This is smaller than the number of DMRSavailable for PDSCH decoding (PDSCH has 12 since it is sent in RBpairs). This leads to degraded channel estimation performance which inturn leads to degraded DL E-PDCCH performance with early decoding whencompared to PDSCH decoding performance. Typically, E-PDCCH decodingperformance should be better than PDSCH decoding as E-PDCCH containscritical control information and no HARQ support. Therefore, mechanismsthat improve E-PDCCH early decoding are required.

E-PDDCH early decoding performance is degraded with the current DMRSstructure due degraded channel estimation. This can be compensated bysending E-PDCCH with a smaller encoding rate i.e., by allocating moreREs for E-PDCCH transmission. However, this reduces spectral efficiency.An alternative solution is to modify the DMRS transmission structure forRBs in which E-PDCCH is sent such that UE receives more DMRS REs perslot. More specifically, to improve the performance of early decoding ofDL E-PDCCH, DMRS RE mapping in RBs where E-PDCCH is transmitted can bemodified so that 12 DMRS REs per antenna port per RB are available tothe UE in the 1^(st) slot. Options for modifying the DMRS structure aredescribed below.

In FIG. 7, a DMRS Structure for EPDCCH RBs is changed in E-PDCCH RBssuch that 12 REs are available for each of the antenna ports R7 and R8 a1^(st) slot and 12 DMRS REs are available for each of the antenna portsR9 and R10 in a 2^(nd) slot. With this structure up to 2 DL E-PDCCHs canbe sent in the first slot, one E-PDCCH on each antenna port 7 and 8. Thesecond slot can be used for UL E-PDCCH transmission with up to 2 ULE-PDCCHs, one E-PDCCH on each antenna port 9 and 10. When compared tothe prior art DMRS structure, the DMRS structure in FIG. 7 providesimproved channel estimation performance when early decoding is used forDL E-PDCCH. However, the number of DL E-PDDCHs that can be multiplexedin a PRB (with length 2 Walsh code) is reduced from 4 to 2. Also, if thesecond slot is allocated for PDSCH to the same UE, a different channelestimation scheme must be used for decoding PDSCH in RBs with DLE-PDCCH. In this embodiment, the EPDDCH RB comprises a first offrequency carriers and the PDCCH RB comprises a second set of frequencycarriers and the second set of frequency carriers do not overlap withthe first set of frequency carriers.

Generally, the UE can receive configuration signaling from the baseunit, indicating to the UE, a set of RBs in a subframe that the UEshould monitor for control channel signaling. For example, the controlchannel signaling can correspond to EPDCCH signaling. The set of RBs canbe called control channel candidate set of RBs. Monitoring impliesattempting to decode various control channel candidates in the controlchannel candidate set of RBs. To receive downlink control information(DCI) in the subframe, the UE has to successfully decode, at least onecontrol channel candidate, in one or more RBs of the control channelcandidate set of RBs. The configuration signaling from the base unit canbe sent to the UE in the form of a radio resource control (RRC) messageor, medium access control (MAC) layer message or a message sent on thePDCCH. Alternately, a UE can receive the configuration signaling inbroadcast message such as a System Information Block (SIB) or a MasterInformation Block (MIB) in LTE systems. Typically, the masterinformation block (MIB) is sent on the Physical Broadcast CHannel(PBCH), which in case of LTE Release-8 is sent on subframe 0 of a radioframe.

In one embodiment, a UE receives a first set of pilot signal resourceelements and control information in one or more spatial layers in afirst resource block in a subframe, wherein the first resource blockspans a set of time symbols in a sub-frame and a first set of frequencycarriers in the sub-frame. The UE also receives a second set of pilotsignal resource elements and data in one or more spatial layers in asecond resource block in the subframe, wherein the second resource blockspans the same set of time symbols in the sub-frame and a second set offrequency carriers in the sub-frame. In FIG. 7, the subframe has onlyfirst and second slots, wherein the first and second resource blocksboth span the set of time symbols in the first slot, wherein the firstand second resource blocks share common time symbols in the first slot,identified as slot 0. FIG. 7 illustrates that the UE receives thecontrol information using only the first set of pilot signal resourceelements.

The UE decodes the one or more spatial layers in which the controlinformation is received using the first set of pilot signal resourceelements in the first resource block, the first set of pilot signalresource elements comprising a first number of pilot signal resourceelements per layer. The UE also decodes the one or more spatial layersin which the data is received using the second set of pilot signalresource elements in the second resource block, the second set of pilotsignal resource elements comprising a second number of pilot signalresource elements per layer. The first number is greater than the secondnumber. In FIG. 7, the first number of pilot signal resource elementsper layer is a first number of pilot signal resource elements per layerper resource block, and the second number of pilot signal resourceelements per layer is a second number of pilot signal resource elementsper layer per resource block. Decoding the one or more spatial layers inwhich the control information is received using the first set of pilotsignal resource elements includes performing channel estimation based onthe first set of pilot resource elements. The UE generally decodes theone or more spatial layers in which the data is received in the secondresource block using the control information that the UE has decoded inthe one or more spatial layers in the first resource block.

In one implementation, the UE decodes a spatial layer in which thecontrol information is received using the first set of pilot signalresource elements in the first resource block, the first set of pilotsignal resource elements comprising the first number of pilot signalresource elements per layer, wherein the first set of pilot signalresource elements is associated with a first antenna port. The UEdecodes a spatial layer in which the data is received using the secondset of pilot signal resource elements in the second resource block, thesecond set of pilot signal resource elements comprising the secondnumber of pilot signal resource elements per layer, wherein the secondset of pilot signal resource elements is also associated with the firstantenna port. For example, considering the subframe structure shown inFIG. 7, if a UE expects that control information (in EPDCCH) is sent ina spatial layer in RB0 and, the spatial layer is mapped to antenna port7, the UE can use the set of pilot signal resource elements associatedwith antenna port 7 in RB0 (marked R7/R8 in the figure) to decode thecontrol information sent in the spatial layer. In this case, the set ofpilot signal resource elements associated with antenna port 7 comprises12 pilot signal resource elements due to the modified DMRS structureused in the RB (RB0) where control is sent. Further, if the UEdetermines that data (in PDSCH) is sent in a spatial layer in RB2 and,the spatial layer is mapped to antenna port 7, the UE can use the set ofpilot signal resource elements associated with antenna port 7 in RB2(marked R7/R8 in the figure) to decode the control information sent inthe spatial layer. In this case, the set of pilot signal resourceelements associated with antenna port 7 comprises 6 pilot signalresource elements as the legacy DMRS structure (i.e., LTE Rel10) used inthe RB (RB2) where data is sent. The UE can determine the set of RBs onwhich control information is expected based on configuration signalingfrom the eNB. It should be noted that, if data is sent to the UE inmultiple spatial layers in RB2, for example, in two spatial layers, onemapped to antenna port 7 and another mapped to antenna port 8, the UEcan use the set of pilot signal resource elements associated withantenna port 7 to decode data in the spatial layer mapped to antennaport 7 and, it can use the set of pilot signal resource elementsassociated with antenna port 8, to decode the data in the spatial layermapped to antenna port 8. That is, on a per spatial layer basis, it canuse 6 pilot signal resource elements per layer in RB2 to, decode thedata.

In another implementation, the UE decodes a spatial layer in which thecontrol information is received using the first set of pilot signalresource elements in the first resource block, the first set of pilotsignal resource elements comprising the first number of pilot signalresource elements per layer, wherein the first set of pilot signalresource elements is associated with a first antenna port and a secondantenna port. The UE also decodes a spatial layer in which the data isreceived using the second set of pilot signal resource elements in thesecond resource block, the second set of pilot signal resource elementscomprising the second number of pilot signal resource elements perlayer, wherein the second set of pilot signal resource elements isassociated with a third antenna port. The first set of pilot signalresource elements and the second set of pilot signal resource elementsoccupy common time symbols in the subframe. In one embodiment, the firstantenna port is the same as the third antenna port and in anotherembodiment the first and third antenna ports are different. For example,if control information (in EPDCCH) for a UE is sent in a spatial layerin a first RB and, the spatial layer is mapped to two antenna ports,antenna port 7 and antenna port 9, the UE can use a first set of pilotsignal resource elements associated with both the antenna ports todecode the control information sent in the spatial layer. In this case,since the spatial layer in the first RB is mapped to two antenna ports,the number of pilot signal resource elements in the first set is equalto the sum of the number of pilot signal resource elements associatedwith antenna port 7 and the number of pilot signal resource elementsassociated with antenna port 9. If data is sent for the UE in a spatiallayer in a second RB and, the spatial layer is mapped to one antennaport, antenna port 7, the UE can use a second set of pilot signalresource elements in the second RB associated with antenna ports 7 todecode the data sent in the spatial layer. Assume RB0 with the DMRSstructure in FIG. 2 as the first RB and RB2 with the DMRS structure inFIG. 2 as the second RB. Considering RB0, 6 pilot signal resourceelements are associated with antenna port 7 and, 6 pilot signal resourceelements are associated with antenna port 9. Therefore, with thisimplementation, the UE can use 12 pilot signal resource elements todecode control information sent in a spatial layer in RB0. ConsideringRB2, 6 pilot signal resource elements are associated with antenna port7. Therefore, the UE can use 6 pilot signal resource elements to decodedata sent in a spatial layer in RB2. More generally, with thisimplementation, to decode control information in a spatial layer in afirst RB, the UE can assume a first spatial layer to antenna portmapping (e.g., one spatial layer mapped to two antenna ports) and, toreceive data in a spatial layer in a second RB, the UE can assume asecond spatial layer to antenna port mapping (e.g. one spatial layermapped to one antenna port). With this implementation, the number ofpilot signal resource elements that the UE can use to receive controlinformation in a spatial layer in an RB is increased without modifyingthe DMRS structure in the RB. In an alternate implementation, controlinformation (in EPDCCH) for a UE is replicated and transmitted on twospatial layers in a first RB with the first spatial layer associatedwith a first antenna port (e.g., antenna port 7) and the second spatiallayer associated with a second antenna port (e.g., antenna port 9). Thereplication of the control information on the two spatial layers resultsin effective single layer for the control information. The effectiveprecoding on the control information is the sum of the precoding appliedfor the first spatial layer on the first antenna port and the precodingon the second spatial layer on the second antenna port. The UE can thususe a first set of pilot signal resource elements associated with boththe antenna ports to decode the control information sent in the twospatial layer. The number of pilot signal resource elements in the firstset is equal to the sum of the number of pilot signal resource elementsassociated with antenna port 7 and the number of pilot signal resourceelements associated with antenna port 9.

In another embodiment, the UE receives a third set of pilot signalresource elements and data in one or more spatial layers in a thirdresource block in the subframe, wherein the third resource block spans asecond set of time symbols in the sub-frame and the first set offrequency carriers in the sub-frame. Here, the second set of timesymbols in the sub-frame is different than the first set of time symbolsin the subframe. In FIG. 7, the first resource block is in slot 0spanning time symbols 0-6 and the third resource block is in slot 1spanning time symbols 7-13. In this embodiment, the first and thirdresource blocks share the first set of frequency carriers. According tothis embodiment, the UE decodes the one or more spatial layers in whichthe data is received in the third resource block using the third set ofpilot signal resource elements, the third set of pilot signal resourceelements comprising a third number of pilot signal resource elements perlayer wherein the third number is at least equal to or greater than thefirst number. In one implementation, the third number is equal to twicethe first number.

The modified DMRS structure of FIG. 8 is similar to the embodiment ofFIG. 7 for the 1^(st) slot. However the 2^(nd) slot of FIG. 8 isdifferent as follows: Instead of remapping the DMRS REs in slot 1 toantenna ports 9 and 10, the DMRS REs are used for antenna ports 7 and 8.With this structure, 2 DL E-PDCCHs can be sent in the first slot(E-PDCCH on each antenna ports 7 and 8). The second slot can be used forUL E-PDCCH transmission or for PDSCH transmission. When an RB pair isused to transmit E-PDCCH and PDSCH (e.g., using antenna port R7) for thesame user, then for PDSCH demodulation, the UE can use 12 DMRS REsavailable in 1^(st) slot RB and 12 DMRS REs available in 2^(nd) slot RBfor channel estimation. Alternatively, the UE may use six DMRS REs inthe 1^(st) slot and six DMRS REs in the 2^(nd) slot. With this option,DMRS structure for PDSCH demodulation for antenna port 7 and antennaport 8 is not changed from LTE Rel-10).

When compared to the prior art DMRS structure, the DMRS structure ofFIG. 8 provides improved channel estimation performance when earlydecoding is used for DL E-PDCCH. When compared to the DMRS structure ofFIG. 7, it is easier for UE implementation to handle PDSCH decoding inslot 1 (i.e., same DMRS mapping can be assumed in RB pairs containingE-PDCCH and RB pairs containing PDSCH). However, when compared tocurrent Rel-10 DMRS structure, in the modified DMRS structure of FIG. 8the number of ports (e.g., number of DL EPDCCH) that can be multiplexedin a PRB-pair (with length 2 Walsh code) is reduced from 4 to 2. Also,if the 2^(nd) slot is allocated for PDSCH to the same UE (instead of anE-PDCCH to same or different UE) the maximum number of PDSCH layers forsecond slot is restricted to 2. Pilot overhead is also increased.

While the discussion so far considers transmissions using 4 antennaports 7, 8, 9, 10 that are sent to the UE using length 2 Walsh codes (intime-domain), it can be extended to cover 8 antenna ports 7, 8, 9, 10,11, 12, 13, 14 with length 4 Walsh codes.

For the modified DMRS structures of both FIGS. 7 and 8, the aspect of aUE receiving two different RBs (one RB for E-PDCCH and one RB for PDSCH)occupying same time symbols with different pilot structure for the sameantenna port was not needed in current and legacy 3GPP systems since theUE was expected to receive only PDSCH using DMRS and PDSCH was alwaysassigned using RB pairs. However, for LTE Rel-11, the UE is expected toreceive both E-PDCCH and PDSCH in the same set of time symbols. IfE-PDCCH is restricted to 1^(st) slot only (this is desirable for earlydecoding), the new DMRS structures in FIGS. 7 and 8 are beneficial forenhanced channel estimation.

If E-PDCCH is sent in 1st slot (slot 0) of an RB pair in a subframe andif the 2^(nd) slot (slot 1) of the RB pair in the subframe is allocatedfor PDSCH, and if the UE can assume that MU-MIMO (Multi-user MIMO)operation is not performed on the E-PDCCH in 1^(st) slot, then up to 5layers can be supported for PDSCH in the 2^(nd) slot using a subset ofthe length-4 OCC (Orthogonal Cover Code) on both reference signal CDMgroups. In FIG. 2, CDM group 1 corresponds to set of reference signalresource elements on subcarrier 0, 5, 10 in a RB-pair (e.g., RB0 andRB2) and CDM group 2 corresponds to set of reference signal resourceelements on subcarrier 1, 6, 11 in a RB-pair. CDM group 1 is associatedwith antenna port 7, 8, 11, 13 using length-4 OCC (e.g., Walsh) in thetime-domain while CDM group 1 is associated with antenna port 9, 10, 12,14 using length-4 OCC (e.g., Walsh) in the time-domain. The OCC code foran antenna port may be permuted (e.g., time-reversal) on differentsubcarriers in the RB-pair. Supporting up to 5 layers for PDSCH in the2^(nd) slot, however, would require a different layer-to-antenna portmapping for layers 2-4 than Rel-10 for such RBs with PDSCH on 2^(nd)slot.

For example if E-PDCCH based on DMRS REs associated with antenna port 7is received by the UE in a first RB of an RB pair in the first slot of asubframe, the possible PDSCH layer to antenna port mapping methods forreceiving a second RB of the same RB pair in the second slot of thesubframe are as follows

2 PDSCH layers: ports 7, 8

3 PDSCH layers: ports 7, 8, 10

4 PDSCH layers: ports 7, 8, 10, 14

5 PDSCH layers: ports 7, 8, 10, 13, 14.

TABLE 1 Antenna ports useable for PDSCH in 2^(nd) slot given EPDCCHreceived in in 1^(st) slot using antenna port 7 (no MU for EPDCCH)EPDCCH/PDSCH spatial layer Antenna port p [ w _(p)(0) w _(p)(1) w_(p)(2) w _(p)(3)] mapping 7 [+1 +1 +1 +1] Usable for PDSCH using thelength 4 Walsh code in right column in both slots (E-PDDCH also receivedusing antenna port 7 but in in 1^(st) slot only using (+1, +1)). 8 [+1−1 +1 −1] Usable for PDSCH using the length 4 Walsh code in right columnin both slots 9 [+1 +1 +1 +1] Not usable for PDSCH 10 [+1 −1 +1 −1]Usable for PDSCH using the length 4 Walsh code in right column in bothslots 11 [+1 +1 −1 −1] Not usable for PDSCH 12 [−1 −1 +1 +1] Not usablefor PDSCH 13 [+1 −1 −1 +1] Usable for PDSCH using the length 4 Walshcode in right column in both slots 14 [−1 +1 +1 −1] Usable for PDSCHusing the length 4 Walsh code in right column in both slots

Further, with no restriction on the UE for which PDSCH is scheduled inthe second slot, a reduced rank transmission (<=4) (with fixed set ofports 8,10, 13 and 14) can be supported in RBs overlapping with EPDCCH.i.e, EPDCCH can be allocated to UE1, and PDSCH can be allocated to anyUEx with up to rank 4 transmission. This imposes a minor schedulingrestriction at the eNB, which is not a significant constraint.

In one embodiment, the UE is configured to receive control information(e.g. EPDCCH) in a plurality of resource blocks in a sub frame. The UEdecodes control information based on a first antenna port, in one of theplurality of resource blocks in a first slot of the subframe. The UEdetermines its data allocation (e.g. PDSCH allocation) based on thedecoded control information. The data allocation can be determined as aset of resource blocks. The UE then can determine a first set ofresource blocks in the second slot of the subframe that are notoverlapping with the plurality of resource blocks for which it isconfigured to receive control information. The UE can then decode (ordemodulate) data (PDSCH) in the first set of resource blocks using afirst set of preconfigured antenna ports. The UE can also determine asecond set of resource blocks in the second slot of the subframe thatare overlapping with the plurality of resource blocks for which it isconfigured to receive control information. The UE can then decode (ordemodulate) data (PDSCH) in the second set of resource blocks using asecond set of preconfigured antenna ports where the second set ofpreconfigured antenna ports are different from the first set ofpreconfigured antenna ports. In one implementation, the first set ofpreconfigured antenna ports can correspond to antenna port sets {7},{7,8}, {7,8,9}, {7,8,9,10} for rank 1,2,3 and 4 transmissionrespectively. The second set of preconfigured antenna ports cancorrespond to antenna port sets {8}, {8,10}, {8,10,13}, {8,10,13,14} forrank 1, 2, 3 and 4 respectively. The UE can further determine a set ofresource blocks in which it can receive both control and datatransmissions and, for the determined set of resource blocks, the UE canuse a third set of preconfigured antenna ports for receiving data. Thethird set of preconfigured antenna ports can correspond to one or moreof the antenna port sets {7}, {7,8}, {7,8,10}, {7,8,10,13},{7,8,10,13,14} for rank 1, 2, 3, 4 and 5, respectively.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession and enabling those ofordinary skill to make and use the same, it will be understood andappreciated that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

1. A method in a wireless communication terminal, the method comprising:receiving a first set of pilot signal resource elements and controlinformation in one or more spatial layers in a first resource block in asubframe, the first resource block spanning a set of time symbols in asub-frame and a first set of frequency carriers in the sub-frame;receiving a second set of pilot signal resource elements and data in oneor more spatial layers in a second resource block in the subframe, thesecond resource block spanning the set of time symbols in the sub-frameand a second set of frequency carriers in the sub-frame; decoding theone or more spatial layers in which the control information is receivedusing the first set of pilot signal resource elements, the first set ofpilot signal resource elements comprising a first number of pilot signalresource elements per layer; decoding the one or more spatial layers inwhich the data is received in the second resource block using the secondset of pilot signal resource elements, the second set of pilot signalresource elements comprising a second number of pilot signal resourceelements per layer, the second number of pilot signal resource elementspresent in the second resource block; wherein the first number isgreater than the second number.
 2. The method of claim 1, wherein thefirst number of pilot signal resource elements per layer is a firstnumber of pilot signal resource elements per layer per resource block,wherein the second number of pilot signal resource elements per layer isa second number of pilot signal resource elements per layer per resourceblock.
 3. The method of claim 1, wherein the second set of frequencycarriers are non-overlapping with the first set of frequency carriers.4. The method of claim 1, wherein a size of the second set of frequencycarriers is same as a size of the first set of frequency carriers. 5.The method of claim 1, decoding the one or more spatial layers in whichthe control information is received using the first set of pilot signalresource elements includes performing channel estimation based on thefirst set of pilot resource elements.
 6. The method of claim 1, thefirst resource block spanning the set of time symbols in a first slot ofthe sub-frame, the second resource block spanning the set of timesymbols in the first slot of the sub-frame, wherein the subframe hasonly first and second slots.
 7. The method in claim 1 further comprisingreceiving a third set of pilot signal resource elements and data in oneor more spatial layers in a third resource block in the subframe, thethird resource block spanning a second set of time symbols in thesub-frame and the first set of frequency carriers in the sub-frame,decoding the one or more spatial layers in which the data is received inthe third resource block using the third set of pilot signal resourceelements, the third set of pilot signal resource elements comprising athird number of pilot signal resource elements per layer wherein thethird number is at least equal to the first number, second set of timesymbols in the sub-frame different than the first set of time symbols inthe subframe.
 8. The method in claim 7, wherein the third number isequal to twice the first number.
 9. The method of claim 1, decoding aspatial layer in which the control information is received using thefirst set of pilot signal resource elements, the first set of pilotsignal resource elements associated with a first antenna port, decodinga spatial layer in which the data is received using a second set ofpilot signal resource elements, the second set of pilot signal resourceelements associated with the first antenna port.
 10. The method of claim9, wherein the first set of pilot signal resource elements and thesecond set of pilot signal resource elements occupy common time symbolsin the subframe.
 11. The method in claim 9, receiving controlinformation using only the first set of pilot signal resource elements.12. The method of claim 1, decoding a spatial layer in which the controlinformation is received using the first set of pilot signal resourceelements, the first set of pilot signal resource elements associatedwith a first antenna port and a second antenna port, decoding a spatiallayer in which the data is received using the second set of pilot signalresource elements, the second set of pilot signal resource elementsassociated with a third antenna port.
 13. The method of claim 12,wherein the first set of pilot signal resource elements and the secondset of pilot signal resource elements occupy common time symbols in thesubframe.
 14. The method of claim 12, wherein the first antenna port isthe same as the third antenna port.
 15. The method in claim 1,determining that data is expected in the second resource block in thesubframe using the control information, decoding the one or more spatiallayers in which the data is received in the second resource block usingthe control information.
 16. The method in claim 1 further comprisingdetermining that control information is expected in the first resourceblock in the subframe based on a signal received from a base unit.